The present disclosure relates to certain polyestercarbonate copolymers having a combination of high scratch resistance and weatherability. Also disclosed herein are methods for preparing and/or using the same.
Polycarbonates are synthetic thermoplastic resins derived from bisphenols and phosgenes, or their derivatives. They are linear polyesters of carbonic acid and can be formed from dihydroxy compounds and carbonate diesters, or by ester interchange. Polymerization may be in aqueous, interfacial, or in nonaqueous solution.
Lightweight thermoplastic materials that have a glossy or semi-gloss finished appearance are useful materials of construction for a wide variety of molded products such as medical devices, radio and TV bezels (i.e. grooved rims for holding glass or plastic panes such as lenses, tuning dials, and other indicating devices), mobile phone keypads, notebook computer housings and keys, optical display films, automotive parts, and other electronic and consumer products. Polycarbonate-based materials, with their high surface gloss capability, high transparency, and excellent impact strength, are useful for such applications.
Such applications expose the molded product to indoor and outdoor conditions of light and moisture. Thus, weatherability, such as color stability and surface finish, is typically desired. Weatherable polycarbonates, however, may have lower ductility and decreased flow properties, and are thus less desirable for use in some applications where high ductility and thermoformability are useful.
Scratch resistance is also useful for molded products or articles whose exterior surface may be subject to physical contact by other objects. For example, everyday activities which can scratch an article may include sliding on a surface, dropping, and rubbing against other items such as coins or keys when placed in a pocket. Polymer compositions with scratch resistance are therefore desirable in articles requiring a durable surface finish and appearance.
In particular, polycarbonates based on bisphenol-A (BPA) have limited scratch resistance. The introduction of scratches causes loss of optical properties, such as transparency in clear compositions and haze or gloss in opaque compositions. Scratches also decrease the aesthetic appeal of a product.
One method of preventing or minimizing scratch damage is to apply a hardcoat to an article formed from a BPA polycarbonate. This hardcoat requires another manufacturing step, adding additional cost to the article.
Another method is to use a scratch-resistant material made from a copolymer of BPA and dimethyl bisphenol cyclohexane (DMBPC). These copolymers have excellent scratch resistance, but decreased impact properties and ductility compared to BPA homopolymers. DMBPC homopolymers have a 6-fold increase in scratch resistance compared to polycarbonates based on BPA and up to a 2-fold increase compared to a BPA-DMBPC copolymer, based on the pencil hardness scale. However, DMBPC homopolymers also have decreased impact properties and ductility compared to polycarbonates based on BPA.
It would be desirable to provide a polycarbonate composition that has a combination of high scratch resistance and weatherability, while maintaining other physical properties such as flow characteristics, haze, and light transmittance.